Radio telegraph system



March 12, 1929. sc M T 1,705,211

RADIO TELEGRAPH SYSTEM Filed Aug. 28, 1924 2 Sheets-Sfieet 1 Wm. Z,

i020 revive 7515771222277.

a 55% Q I 61mm;

March 12,1929. L, R SCHMTT 1,705,211

RADIO TELEGRAPH SYSTEM Filed Aug. 28, 1924 2 Sheets-Sheet gwuenkoz i an 21 22:! 7?, 62/272??? aw 5M flumm Patented Mar. 12, 1929.

U NITED STATES v LAwREiicE R. SCHMITT, or. ciiicaeo, ILLINOIS, ASSiGNQLt mo M RKRUM COMPANY or cnicAeo, rumors A CORPORATION OE I-1 ,L i

BA-DID TELEGRAP sYsT Application filed August 28, 1924 "Serial No. I

Myinvention relates broadly to radio telegraph systems, and more particularly to a system of telegraphic printing without the use of interconnecting wires between the transmitting and receiving stations.

One of the objects of my invention is to provide a radio telegraph system "for the printing of characters where'the relay system at the receiving station may be positively actuated both upon the marking and spacing contacts of the relay, eliminating the dependency of the relay system upon spring actuationfor either the marking or spacing contact operation.

Another object of my invention is to provide a multi-frequency radio telegraph system where marking and spacing signals may be radiated from a transmitting station-to positively actuate a relay system at a receiving station connected with automatic printing apparatus Still another object of my invention is to provide a multi-frequency radio printing telegraph system where a pair of slightly separated Waves are employed'contained Within a relativel narrow band of frequencies and adapted it be radiated'and received at a receiving stationin selectivelytuned discriminating circuits where the signals may independently operate a relay system for actuating automatic printing apparatus.

A further object of my invention is to proyide a multifrequency radio telegraph system for printing messages where the Wave band employed is relatively narrow but which contains distinct signaling frequencies for marking and spacing signals adapted to be received in the same tuned circuit at a receiving station and separated in tone frequency to a degree necessary to enable the marking and spacing signals to independently actuate a relay system arranged to control an automatic printer.

l A still further object of my invention is to provide circuit arrangements at both transmitting and receiving stations whereby the transmission of signals may be automatically controlled by radiating energy through one or more ofa definite number of successive time intervals onseparated wavelengths for each character transmitted with circuit arrangements at the receiving station for re: ceiving the energy thus transmitted, and

selectively discriminating between the en ergy transmitted at one frequency and the energytransmitted "at; another frequency comprising'a particular character whereby automatic printingapparatus maybe positively actuated for printing a character corresponding'to the signal energy thus transmitted. 'lhe invention also'eontemplates the provision of a balanced receiving relaysystem for the reduction or substantial'elimination of static and other interfering signals which normallyoperate a relay at-a radio receiving station and introduce complications in radiov printer systems. v i

My invention will'be more clearly under- .stood by reference'to the following specification and the accompanying drawings, in which": 3 Figure 1 is a diagrammatic illustrationof a radio transmitting station showing the electrical connections'embodying the princi' plelof my invention; Fig.-2 shows a sche-- matic arrangement of a receiving apparatus and thewiring arrangement of the discriminating, circuit of my invention; Fig. '3 is a modified arrangement of a transmitting circuit showing an application of my multifrequen'cy radio'teleg'raph system to carrier wave systems Where the carrier is modulated at separated frequencies for producing the marking and spacing signals; and Fig. 4 shows an arrangement of my multi-frequency radio telegraph system as applied to a continuous wave transmitter With the keying circuit arranged to shift the frequency of the transmitted signalfor differentiating the marking and spacing signals transmitted.

invention makes use of a five-unit code wherethe signaling energy extends overa given unit oftime which'is divided into five intervals, during each ofwhich energy may be radiated at one frequency or another to;

produce different combinations of-multifrequency signals each extendingv over the same unit of time, p

Heretofore in radio telegraph operation of automatic printer systems it hasbee'n the practice to transmit a signaling character extending over afgiven unit of, time and divided into five intervals ofrt iine, during each of which energy may or maynot be transmitted. "In -thistype of systemlthe relay apparatus at the distant receiver must be actuated by either the current or noncurrent interval and the return of the relay tongue to either the marking or spacing contact has been dependent upon spring actionor local electrical bias,'with the inherent- ;disadvantages of mechanical inertia of the parts. In a system of this kind I have deapparatuslVith these disadvantages in mind I have developed the invention described herein. 1

The fundamental principles of this sys- A tem may be broadly explained by' consid'ering a radio transmitter of-the continuous wave'type adjusted so ,as to give one wave,"

say 230.50 kilocycles. as a marking waveor signal and another Wave separated from the marking wave by two hundred and fifty or more cycles, say 230.25 kilocycles as a spacpable of receiving continuous wavesembrao' ing both frequencies as radiated on the 1 marking and spacing waves. A special re-' lay circuit, which will be more fully described hereinajfter, is coupled tothe receiver and operates to separate this markingsignal from .the spacing signal wherebyone dot and dash code employing a compensasignal pulls the tongue of a polar relay to one side on the marking wave and to the other side on the spacing wave. The relay' circuit is adjusted to selectively discriminate between the marking'and spacing signals, giving positive operation of the control relay in each of two positions.

I am aware that heretofore in the art it has been proposed to signal'by meansof a tion wave. There is a basic difference between this system and such prior'methods which use a compensatin wave, and that is,-

a very slight difmy system functions wit ference of frequency, substantially less than a quarter of a kilocycle, and each charac tcr signal may be composed of a number of time intervals of differing frequency, Whereas dot and dash compensation wave signal-- ing systems have usefully employed only one wave, the other being so'objectionable that many methods have been proposed to suppress such additional wave.

My system permits the transmitter to be tuned so that the marking and the spacingwaves both will not tune as broadly .as the present Wave radiated from a radio broadcastmg station. Other systems using a. compensatlng wave require the two waves to be fairly well separated to be able to reduce the interference between the two signals at the receiver to enable one to be read. 'My system accomplishes the results aswill be herein-described byseparating the audio signal notes instead of the radio frequency waves.

'Only one system-of radio frequency tuning is necessary, thus reducing the number of circuits and their electrical losses.

Referring more particularly to the drawings, reference character 1 designates the transmitting antennae system grounded at 2. The inductance 3 has been shown in electrrcal connection with an oscillator formed by the parallel connection of electron tubes 4 and-5. The oscillator circuit is formed by linking the input and output circuits of electron tubes tand 5 through the transmitting inductance 3. The cathodes of tubes 4 and 5 have been represented as supplied from a suitable source 6 while the'plate potential considerable extent. 1 Connected in shunt with a part 8'of the transmitting inductance ing wave or signal. At the receivin end of the system a receiving set is provided ca-l 3 I haye' shown a keying circuit'9; The keying circuit may consist of an automatic transmitterhaving a plurality of pairs of contacts 10, five sets of "the contacts con-'- trolling thetransmission of signal impulses,

=whilethe other pair of contacts forms a start-stop control for thesignaling system. It willtbe-understood that the contacts 10 may be'icontrolle'dfrom a manual keyboard, vor a traveling tape controller may be employed whereinthe tape is perforated in accordance with the signal characters to be tran'smitte d'and controls the opening and closing of contacts 10 in succession. While: contacts 10 are open the entire inductance 3 is placed in the antenna circuit and there- 'on the shunting of contacts 10, or any one of them in succession, the frequency of the transmitted signal is shifted. In this manner. the given unit-of time over which each signal character extends is divided into sucby referencecharacter 14. "The radio frcquency tuning system is responsive to both frequencies transmitted by antenna system 1 and 2. The received energy is amplified by the-amplifier, represented at '15. A local source of energy is established at the re-- ceiver as represented diagrammatically by reference character 16'and 1s connected wlth therece1v1ng-c1rcu1t forming means for --heterodyning the incoming signaling energy.

The output of the receiving apparatus is represented by conductors 17 which lead to the input circuit of the relay system designated generally by-reference character 18.

'The relay system includes an audio freby controls the frequehcy transmitted. Up-

quency iron core input transformerde signed for high efiiciency over the band "of audio notes employed inthe marking and spacing signals. Reference character 21 designates the primary windin of the input transformer 20' and numerals 22 and 23 represent secondary windings tuned respectively by variable condensers 24 and 25 to the two transmitted frequencies. Two separate transformers may, however, be used in lieu of 'the transformer 20. Filter circuits 26 and 27 comprising inductances 28 and 29 and capacities 30 and 31respectively are inserted in each of the secondary circuits to increase the sharpness of tuning. 32 and designate electron tubes receiving signal 1mpulses on their respective grid electrodes 34 and 35 from circuits 22, 24, 26 and 23, 25, 27. A negative bias is maintained onthese grids by a'variable C battery designated at 36. The plate circuit of tube 32 connecting with plate electrode 37 goes through one coil 38 of the polar relay indicated at 39 and through one coil 40 of the inilli-ammeter 41 to the positive terminal of B battery 42 while the plate circuit of tube 33 connecting avith plateelectrode 43 goes through the opposite coil 44 of the polar relay 39 and through the winding 45 of milli-ammeter 41 to the positive side of B battery 42. Filament rheostats 46 and 47 are used to control the plate current through the two coils 38 and 44 of the relay 39 by regulation of the temperature of cathodes 48 and 49 respectively. Filament heating current is sup-' plied from any desired source designated A in the diagram. 7

i The provision of the split ammeter'circuit enables the relay system to be very accurately balanced so that the relay has a neutral bias. The trap circuits 26 and 27 enable the relay system to accurately discriminate between the marking and spacing signals and tend to screen the circuits against operation by interfering signals. The windings 38 and 44 of polar relay 39 operate upon armature 50 which is mounted midway between coils 38 and 44 and is adapted to swing in either of two directions to close contacts at 51 or 52. The marking and spacing circuits are included between terminals T and M and T and S respectively from which connections are taken to the automatic printer control circuits.

In Figs. 3 and 4, I have shown different methods of securing the double frequency signaling characters. In Fig. 3 transmitter tube 55 connected as an oscillator in the antenna system 1, 2 and 3 and radiates a continuous carrier wave. The carrier is modulated by a second oscillator 56 arranged to produce two audio frequency notes at will in accordance with the transmitting impulses. The input and output circuits of tube 56 are shown interlinked through an inductance 57 with the output circuit thereof coupled with the input circuit of the oscillator 55 through coi s 58 and 59. The audio frequency note therefore, which is generated by tube 56 may be usefully employed to modulate the carrier frequency produced by tube 55 in the production of a signal. In-

ductance-57 is normally shunted by capaci ties 60 and 61 connected in parallel through relay contacts and which may be adjusted to give the desired si'gnalingfrequency for transmission. of the marking or spacing wave. The second condenser 61 is arranged to be disconnected from the parallel circuit condenser 60 by the operation of relay 62 having tongue 63 and contacts 64 and 65.

The tongue 63 is normally drawn over against contact 64 under'the action of spring 69. An armature winding 66 is mounted adjacent the swinging armature 63 and is connected in the keying circuits and attracts the armature tongue 63, whereby the signaling intervals may be divided into a plurality of time intervals of either the tone frequency developed by tube 56 having capacity 60 in circuit, therewith or thetone frequency developedby tube 56 having both relay 62 having. tongue 63 and contact 65' connected with the terminals of loop 68. The relay winding 66 is energized in accordance with the signaling impulses to attract armature 63 against the action of spring 69 breaking the circuit across loop 68 which normally tends to absorb the signaling energy and effectively change the radiated frequency. The control winding 66 is connected as before, in the keying circuit. By the keying circuit it will be under stood that I refer to that type of transmitter control embodying the plurality of contacts designated at 10 in Figure 1, wherein the contacts are actuated by suitable mechanism in succession, particularly pairs of contacts remaining either actuated or unactuated in accordance with the particular combination of impulses comprising that signaling character.

Ihave illustrated but threemethods of transmitting signals by double frequency although there are a number' of other methods which may be used. For example two different audio notes might be transmitted over the usual broadcasting station transmitter, without the necessity of hetero dyning at the receiver. A master oscillator may be employed having itsoutput connected with a power amplifier, the signals,

being produced by keying the master oscillator. F or high power operation alternators may be used at the transmitter and two transmitters installed, tuned to the two waves one sending the marking signal and the otherthe'spacing signal. A high power are transmit-ter may be employed and the absorptive method of keying utilized radiating marking and spacing waves at very slightly separated frequencies.

In the operation of my system a signal sent from the transmitting station using a marking wave of say 230.5 kilocycles, although this maybe any wave length, and a spacing wave of say 230 kilocycles separated from the marking wave by 250 cycles, although this may be more or less. The re ceiving set is tuned to these waves and the v heterodyne is tuned to give a beat note of I is adjusted to reject the 1000 cycle note;

say, 1000 cycles on the marking wave. As

the spacing wave is separated from the.

marking wave by 250 cycles this wave heterodyne will be 1250 cycles or 750 cycles depending on whether the heterodyne is adjusted above, or below the marking wave.

If filter 27 is designed for 1250 cycles, the spacing wave is heterodyned above the marking wave. c j

Adjusting the relay, secondary winding 22 and condenser 24 is tuned to resonance on the 1250 cycle note. Filter 27 is adjusted to reject the 1250 cycle note and filter 26 Therefore, the spacing wave of 1250 cycles will pass through to the grid 34 of electron tube 32 causing a current to flow through circuit 37, 38, 40 and 42 and back to filament 48. Filter 27 and thetuned circuit 23 and 25 rejects this current however, and no current flows in circuits 43, 44, 45, 42, and-back to filament 49 of tube 33. The marking wave of 1000 cycles, for example willhowever pass through circuit 23, 25, 27 to the grid 35 of tube 33 causing a current to flow 'in circuit 43, 44, 45 and 42 and back to filament 49 while this wave is rejected by filter 26 and the tuned circuit 22, 24. This action pulls the relay tongue 50 to one side against contact 52. As the; coils 38 and 44 of the polar relay 39 are wound in opposition it can readily be seen that static or other interfcrence will go through both tuned circuits 2224' and 23-25 and both filter circuits 26 and 27, with equal intensity, if at all, and as the plate circuits 37 38 and 43-44 have been balanced by filament rheostats, 46 and 47, will have substantially no effect on the relay 39. A

It will be understood that while I have desc'ribedmy invention in connection with a single printer channel that this multiple frequency teleggaph' system may be operated as a. duplex transmitter formultiplex twochannel transmission by using four transmitted frequencies instead of two as herein described. In practice A channel would operate on t o-separated frequencies after detection an being heterodyned for example at 800 cycles for marking and 100 cycles for the spacing wave while B channel would work on 1300 cycles and 1500 cycles for marking and spacing respectively at the transmitter station. These four fre-\ quencies mayi be controlled by two automatic multiplex transmitters and. a distributor while at the various receiving stations onl regular-start stop printers would be used: In this waytwo-channel transmission can be carried on from one transmitting station with A and B channel receivers widely separated. 'It will be understood, that with the system herein described relay operation of apositive character without me chanical' or local electricalbias is obtainable and by reason of the sharpness and clear definition of the signaling impulses obtainable, I am enabled to operate the systern at relatively high speed with accuracy.

While I have selected certain particularembodiments by which to illustrate my invention, I desire 'it to be understood that that modification may be made and that no \limitations upon the invention are intended other than are imposed by the scope of the appended claims. 7 Having thus described my invention, what I claim and desire to secure by Letters Patent of the United States is as follows:

l 1. A radio telegraph system for transmit V ting-and receiving messages in print, com-, prising in combination means at a transmitting station for radiating one or another firequency in succession within limits of 250 cygles, a common tuned circuit for receiving 'the severalfrequencies, and means connected to said common tuned circuit for closing a plurality of circuits corresponding to the ,number of transmitted frequencies for controlling a circuit to an automatic printer.

2. A radio telegraph system for transmittingand receiving messages in print, comprising in combination at the transmitter a generator of continuous Waves, means for radiating energy developed by said generator, means for shifting the frequency of the radiated energy with'n a limit of 250 cycles through each of a ,c'efinite number of successive time intervals whereby each signaling character consists of a plurality of frequencies; at the receiving station a common tuned circuit responding to all of the plurality-of frequencies comprising each character, a circuit connected to said common tuned circuit for discriminating be tween said frequencies, and means independently operated by each of said last mentioned circuits for positively controlling circuits to an automatic printer.

3. A radio tele raph system for receiving messages, directly in print, comprising in combination receiving apparatus adapted to respond selectively to a plurality of frequeneies Within a range of 250 cycles, means connected to said apparatus for discriminating between said frequenmes, means independently connected in circuit With said aforemention means and adapted to respond independently to one or another of said frequencies for controlling a circuit to an automatic printer.

LAWRENCE R. SCHMITT. 

